An ordered three-dimensional (3D) microstructure is an ordered 3D structure at the micrometer or nanometer scale. 3D microstructures can be manufactured from polymer materials such as polymer cellular materials. Currently, polymer cellular materials that are mass produced are created through various foaming processes, which all yield random (not ordered) 3D microstructures. 3D microstructures may also be known as “micro-trusses.”
A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. When a monomer that is photo-sensitive is exposed to light (e.g., UV light) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region due to the index of refraction change, further advancing that polymerized region. This process will continue, leading to the formation of a waveguide structure with approximately the same cross-sectional dimensions along its entire length.
For example, self-propagating polymer optical waveguide systems based on thiol-ene polymerization, are described in U.S. Pat. No. 8,017,193 issued Sep. 13, 2011 to Zhou and Jacobsen at HRL Laboratories, LLC in Malibu, Calif., United States. This patent describes formation of a polymeric micro-truss structure using monomer formulations appropriate for a thiol-ene system. This system produces high molecular weight by an alternating reaction between a thiyl radical reacting with a terminal unsaturated group followed by the reaction of a hydrogen radical with the carbon-centered radical to regenerate a thiyl radical and begin the process again.
In some commercial applications, it is necessary to join a thermoplastic polymer to a thermosetting polymer. Prior art exists for fusion welding of two thermoplastic polymer materials, but attachment of a thermoplastic material to a thermosetting polymer is not possible using conventional methods. Consequently, several different methods have recently been developed for forming a thermoset-thermoplastic polymer joint.
Thermoplastic encapsulation methods are known (see, for example, EP0084631B1). In this approach, a bond is formed between a cured thermoset and a thermoplastic polymer by heating the thermoplastic above its glass-transition temperature, and then letting it flow over or into the thermoset polymer component. This flow coating or encapsulation is not a chemical bond or fusion weld but rather a mechanical attachment formed over a large surface area between the two materials. However, poor bond strengths generally result from simple flow coating or encapsulation. In addition, surface finish, thickness, and appearance of the thermoplastic may be negatively impacted after the joining process.
Co-cure heating methods are known (see, for example, EP1423256B1). In this approach, the joint consists of a thermoplastic polymer and an initially uncured thermosetting polymer component. Heat is then applied to both melt the thermoplastic and cure the thermoset at the same time. If the glass-transition temperature of the thermoplastic and the cure temperature of the thermoset are similar, then both materials will flow upon heating and form a mixed thermoset-thermoplastic interface at the joint. While this approach may provide a joint with superior mechanical strength as compared to the encapsulation method above, its utility is limited because it requires the thermoplastic and thermoset to have very similar glass-transition and cure temperatures, respectively. Additionally, because the thermoset must be thermally cured for this method to work, it cannot be applied to materials with alternative cross-link initiation methods such as the above-described micro-truss structures which use a UV-curable polymer.
Particle-insertion methods may also be employed (see, for example, U.S. Pat. No. 7,645,642). In this approach, functionalized particles (e.g. glass spheres) are inserted into the thermoplastic and thermoset polymer components individually. When the thermoset and thermoplastic components are placed into contact and heated, the spheres melt and flow across the interface, to apparently bond the functionalized glass spheres both to themselves and to the thermoset/thermoplastic materials. Such an approach has an obvious limitation in that it requires a parasitic material phase to be introduced in order to form the bond. Furthermore, these glass particulates may spoil the surface finish and appearance of the thermoplastic material since they must be uniformly loaded throughout the thermoplastic in order for this method to be accomplished.
In the case where the substrate is a thermoplastic and the bonding polymer is a thermoplastic, conventional methodologies for joining two thermoplastic components can be used. One option is to heat the two thermoplastic materials past their glass-transition temperature, apply pressure to promote flow of material across the interface to be bonded, and then cool both components below the glass-transition temperature to solidify the joint. In this method, generally referred to as fusion welding, heating can be accomplished either directly (e.g. with an oven or torch) or indirectly (e.g. RF induction heating, vibration welding, or ultrasonic welding).
Thermosetting materials cannot be joined in this manner, however, since heating of these materials will not result in flow of the material due to the cross-linked nature of a thermoset. Consequently, a cured thermoset-thermoplastic polymer joint cannot be produced using direct or indirect fusion methods in the prior art, a deficiency which needs to be remedied.
It is desired to avoid concurrent melting and curing of the thermoplastic/thermoset interface, as well as to avoid insertion of a third parasitic material phase to form a bonded interface.